The present invention relates to a control unit for controlling a direct-current load, said control unit comprising a DC/DC bridge provided with controllable semiconductor switches, said bridge having two bridge sections, one of which bridge sections conducts direct current while the other one is controlled via PWM to regulate the current magnitude.
Elevator motor drives may be either alternating-current or direct-current motor drives. The drives may be controlled e.g. via PWM (Pulse Width Modulation). Today, alternating-current motor drives are fairly common, especially because of the simple construction of alternating-current motors. However, direct-current motor drives are still in use. Neither is it always appropriate to replace a direct-current motor drive with an alternating-current motor drive, because e.g. gearless direct-current motor drives and the direct-current motors used in them are durable and it is therefore unnecessary to replace them with alternating-current motor drives. Besides, replacing the motor entails relatively high costs.
Since the trend is towards alternating-current motor drives, it is also hardly rational to specifically develop power electronics systems for use in the control of direct-current drives. In addition, semiconductor components, such as IGBTs, used in alternating-current drives are all the time becoming increasingly efficient and economical. Moreover, it is to be expected that especially new regulations concerning network harmonics may alter the situation in future so that the use of traditional thyristor bridges used in direct-current drives will become more difficult.
The object of the invention is to eliminate the drawbacks of prior-art technology and achieve a new type of PWM-controlled control unit for controlling a direct-current load, such as a direct-current motor. The solution of the invention is based on a new principle of power electronics topology, wherein it is possible to utilize the technology of alternating-current drives in the control off direct-current motors. In the solution of the invention, a PWM-controlled bridge section consists of two bridge arms, and the semiconductor switches of the bridge arms are turned alternately into the conducting state.
The preferred embodiments of the solution of the invention are presented in the claims below.
By using the technology of the invention, it is possible to manufacture modern and economical PWM-controlled direct-current motor drives e.g. for elevator applications. By applying the invention, the power electronics technology and components of alternating-current drives manufactured in large production series can be utilized in direct-current drives. The conductor rails and other structures of the power stage can be identical to those used in alternating-current drives. In addition, the use of semiconductor switches, such as IGBTs can be optimized even in direct-current applications. And, in particular, cost savings are achieved in development and production methods as the same methods can be used in both alternating-current and direct-current drives.